JP2013137883A - Laminated fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell stack that emits less formic acid over a long period of time without reducing system efficiency of a fuel cell, and to provide a fuel cell system.SOLUTION: A laminated fuel cell includes a plurality of laminated unit cells each having: a membrane electrode assembly that has a pair of an anode electrode, and a cathode electrode, arranged on two respective sides of an electrolyte; and a pair of separators that are arranged on two respective sides of the membrane electrode assembly. A porous layer is provided on a surface of each of the separators that is to have contact with the anode electrode. In the porous layer, a first formic acid decomposition catalyst layer is formed that includes a catalyst having at least one metal selected from the group consisting of palladium, iridium, rhodium, and alloys of any of the foregoing metals.

Description

  The present invention relates to a fuel cell that includes an anode, an electrolyte membrane, a cathode, and a separator, in which fuel is oxidized at the anode and oxygen is reduced at the cathode. Also, a stacked fuel cell in which a plurality of the fuel cells are stacked. The present invention also relates to a power generation device including such a fuel cell, a small portable power source, and an electric device or electronic device using such a power source.

  In recent years, global warming and environmental pollution problems due to mass consumption of fossil fuels have become serious problems. As a means of coping with this problem, instead of internal combustion engines that burn fossil fuels, fuel cells that use hydrogen, methanol, etc. as fuels, such as solid polymer fuel cells, and oxygen, air containing these, etc. as oxidants are attracting attention. Collecting.

  A fuel cell is a clean and highly efficient power generation system that has less environmental impact of emissions from power generation. In particular, the applicability of a fuel cell as a power source for a mobile device as a high energy density power source has begun to be examined.

  Recent advances in electronic technology increase the amount of information, and it is necessary to process the increased information faster and with higher functionality, so a high power density and high energy density power supply, that is, continuous drive time Need a long power supply.

  There is a growing need for small generators that do not require charging, that is, micro-generators that can be easily refueled. Against this background, the importance of fuel cells is being studied.

  A fuel cell is a generator that consists of at least a solid or liquid electrolyte and two electrodes that induce a desired electrochemical reaction, an anode and a cathode, and converts the chemical energy of the fuel directly into electrical energy with high efficiency. is there.

  In such fuel cells, those using a solid polymer electrolyte membrane as the electrolyte membrane and using hydrogen as fuel are called polymer electrolyte fuel cells (PEFC), and those using methanol as fuel are directly methanol. It is called a direct fuel fuel cell (DMFC). Among them, DMFCs that use liquid fuels are attracting attention as being effective as small portable or portable power sources because of the high volumetric energy density of the fuel.

  In DMFC, methanol supplied to the anode is oxidized and discharged as carbon dioxide. In addition, methanol that has permeated the solid polymer electrolyte from the anode and moved to the cathode is oxidized by oxygen supplied to the cathode and discharged as carbon dioxide. In these methanol oxidation processes, a considerable amount of formic acid as an intermediate product is generated and discharged from the fuel cell. Since this formic acid is harmful to the human body, its amount needs to be reduced as much as possible.

  As a method for removing formic acid, which is a harmful substance discharged from a fuel cell, there is a method of providing a filter having a by-product gas absorbent in an exhaust gas pipe as described in Patent Document 1, for example. Further, as described in Patent Document 2, there is a method in which a filter containing a formic acid decomposition catalyst is provided in an exhaust gas pipe.

JP 2008-210696A JP 2005-183014 A

  However, the method of providing an absorbent has a limit in the amount of absorbent adsorbed, and it is difficult to obtain a formic acid removal effect over a long period. Also, in the method of installing the catalyst filter in the exhaust gas piping, since the filter serves as a flow resistance of exhaust gas, it is necessary to improve the blower capacity, and the loss due to the auxiliary power increases, so the efficiency of the fuel cell system increases. It will go down.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fuel cell stack and a fuel cell system in which the amount of formic acid emitted is small over a long period of time without reducing the system efficiency of the fuel cell.

The gist of the present invention for achieving the above object is as follows.
A membrane electrode assembly in which a pair of anode and cathode electrodes are disposed on both surfaces of the electrolyte, and a pair of separators disposed on both sides of the membrane electrode assembly as a unit cell, and a stacked type in which a plurality of the unit cells are stacked In the fuel cell, a porous layer is provided on a surface of the separator in contact with the anode electrode, and a catalyst made of at least one metal selected from palladium, iridium, rhodium and an alloy of the metal is provided inside the porous layer. A first formic acid decomposition catalyst layer is formed.

  The separator is provided with a porous layer on a surface facing the cathode electrode, and a second formic acid decomposition catalyst layer containing a catalyst for decomposing formic acid is formed inside the porous layer. To do.

  According to the present invention, it is possible to provide a fuel cell stack and a fuel cell system that have a small amount of formic acid discharged over a long period of time without reducing the system efficiency of the fuel cell.

The expansion | deployment perspective view of the separator which shows a 1st aspect. The development perspective view of the fuel cell using the separator of the present invention. Sectional drawing in AA 'of the separator shown in FIG. The enlarged view of the catalyst layer vicinity shown in FIG. Sectional drawing in AA 'of the separator shown in FIG. Sectional drawing in AA 'of the separator shown in FIG. The enlarged view of the catalyst layer vicinity which formed the metal layer between the separator and the catalyst layer. The enlarged view of the catalyst layer vicinity which formed two metal layers between the separator and the catalyst layer.

  One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a bird's-eye view of a separator 1 showing the first embodiment. However, in order to help understanding, the gasket 5 facing the front and back surfaces of the separator 1 is also shown. The separator 1 has a flat periphery and is formed by extruding and press-forming the central portion to form a flow path. The flat portion 2 is a portion necessary for making the surface contact with the gasket 5, and the flow passage portion 3 is an uneven groove for allowing reaction gas (general name of fuel gas and oxidant gas) and cooling water to flow through the front and back of the separator. It is. Further, a manifold 4 serving as an inlet / outlet for the reaction gas and the cooling water is formed. Two gaskets 5 are in close contact with each other on the flat portion 2 on the front and back surfaces of the separator 1 to constitute a separator 101 with a gasket.

  When the separator 1 according to this embodiment is used in an actual battery, the battery is combined with an MEA (Membrane Electrode Assembly) 7 or the like.

  FIG. 2 shows an example of a battery configuration using the separator according to this embodiment. The separator 101 to which the gasket 5 is bonded is composed of two types. The separator 101 with the gasket for allowing the reaction gas to flow on both sides is represented by the symbol 101A, one side for the reaction gas, and the opposite surface for the cooling water by the symbol 101B. The MEA 7 is sandwiched between the pair of gasketed separators 101A or 101B on the gas flow surface side to form one cell (unit cell). A plurality of the unit cells are stacked, and a fuel cell is configured by tightening both ends using a current collector plate 8, an insulating plate 9, and an end plate 10 connected to an external circuit. The fuel cell membrane / electrode assembly 7, the separator 101, the current collector plate 8, the insulating plate 9, and the end plate 10 are formed with a manifold 4 serving as an inlet / outlet of fuel, oxidant gas, and cooling water. Fuel and oxidant gas are supplied from the manifold 4, and electricity is generated by supplying fuel to the anode and oxidant gas to the cathode through the gas flow path of the separator 101. The waste liquid containing unreacted fuel passes through the gas flow path of the separator 101 and is discharged from the outlet-side manifold 4 to the outside. In addition, a cooling unit for cooling so that cooling water serving as a refrigerant supplied from the manifold 4 flows into the separator in which the flow path for cooling water is formed, and the temperature of the unit cell is within a predetermined temperature range. It becomes. The separator in which the flow path for cooling water is formed may be provided for each unit cell, or one separator may be provided for a plurality of unit cells.

  The separator 1 shown in FIG. 1 is in contact with the anode or cathode of the MEA that is the power generation unit at the apex of the convex surface of the separator 1. Therefore, the convex vertex of the separator 1 needs to have conductivity. If a conductive path from the top of the convex surface to the current collector plate 8 is formed, the surfaces other than the top of the convex surface are irrelevant to the electrical conduction, and therefore do not require conductivity and may be insulating. , May be conductive.

FIG. 3 is a view schematically showing a cross section taken along the line AA 'of the separator 1 shown in FIG.
The porous layer 11 is formed on the outer surface of the separator 1, and the reaction byproduct decomposition catalyst layer 12 is formed in the porous layer 11.

  FIG. 4 is an enlarged schematic view of the vicinity of the reaction byproduct decomposition catalyst layer 12 in the separator cross section shown in FIG. A reaction by-product decomposition catalyst layer 12 is formed in the porous layer 11, and voids remain in the reaction by-product decomposition catalyst layer 12 so that reactants can be supplied.

The reaction by-product decomposition catalyst layer 12 is obtained by kneading a catalyst metal, at least one conductive material such as carbon, conductive ceramics, and metal powder, a binder for fixing the conductive material, and a solvent. It is formed by coating. The catalyst metal can be used as fine particle powder, but is preferably supported as fine particles on a carrier having electronic conductivity.
This is because the catalyst metal can be used as smaller fine particles by being supported on the carrier, and the specific surface area is increased. Further, by being supported on the carrier, it is possible to suppress deterioration in which the catalytic metal aggregates and becomes coarse and the specific surface area decreases. In addition, it is preferable to use a carbon carrier because the carrier having electron conductivity is difficult to corrode. Here, as the carbon support, one having a specific surface area of 10 m ² / g or more is preferably used in order to highly disperse the catalyst metal, and for example, carbon black, carbon nanotube, carbon fiber, activated carbon and the like can be used. .

  In addition, binders include fluorine resins, silicon resins, phenol resins, epoxy resins, polyimide resins, polyamide resins, polyolefin resins, furan resins, rubber resins, and some of these mixtures. Can be used.

  The pore diameter of the porous layer 11 is set according to the size of the catalyst metal and the conductive material constituting the reaction byproduct decomposition functional layer 12, and is set to, for example, 0.1 to 100 μm.

  Although FIG. 4 shows the state of the reaction byproduct decomposition functional layer 12 in the porous layer 11, the reaction byproduct decomposition functional layer 12 may also be formed on the surface of the porous layer 11. At this time, voids are formed in the reaction byproduct decomposition functional layer 12, and the reactant is supplied to the inside of the porous layer 11 through the voids.

With such a configuration, the reaction by-product can be decomposed on the separator surface, and a stacked fuel cell with a small amount of reaction by-product discharged over a long period of time can be provided.
In addition, since the reaction by-product decomposition functional layer 12 is provided inside the porous layer 11, a stacked fuel cell with a small amount of reaction by-product discharged over a long period of time can be obtained from the viewpoint of suppressing the separation of the catalyst metal. Can be provided.

Another embodiment of the present invention will be described. FIG. 5 is a view schematically showing a cross section taken along the line AA 'of the separator 1 shown in FIG. When methanol is used as the fuel, formic acid is generated as a reaction by-product at the anode. The functional layer at the top of the convex surface of the separator 1 includes palladium, which is a catalyst metal, at least one conductive material such as carbon, conductive ceramics, and metal powder, a binder for fixing the conductive material, and a high solid content. The formic acid decomposition catalyst layer 13 having electrical conductivity and proton conductivity was formed by coating after kneading the molecular electrolyte and the solvent.
The formic acid decomposition catalyst layer 13 preferably does not contain a catalyst such as platinum, ruthenium, osmium, tungsten, molybdenum, iron, cobalt, nickel, or manganese that promotes the methanol oxidation reaction. In particular, a composite catalyst of platinum and ruthenium is used. It is preferably not included. When a catalyst for promoting the methanol oxidation reaction is included in the formic acid decomposition catalyst layer 13, an oxidation reaction of methanol also occurs here, and formic acid is generated again as an intermediate product. End up. In addition, since palladium used as a formic acid oxidation catalyst hardly functions as a catalyst for methanol oxidation reaction, new formic acid is hardly generated on palladium. Further, palladium is preferably supported as fine particles on a carrier in the same manner as described above. This is because the catalyst metal can be used as smaller fine particles by being supported on the carrier, and the specific surface area is increased.

  For the solid polymer electrolyte membrane, sulfonated fluoropolymers such as polyperfluorostyrene sulfonic acid and perfluorocarbon sulfonic acid, polystyrene sulfonic acids, sulfonated polyether sulfones, and sulfonated polyethers. A material obtained by sulfonating a hydrocarbon-based polymer such as ether ketones or a material obtained by alkylating a hydrocarbon-based polymer can be used.

  On the anode side, the formic acid decomposition catalyst layer 13 needs to have proton conductivity in order to electrochemically oxidize formic acid. Therefore, it is necessary to use a solid polymer electrolyte membrane having proton conductivity for the binder of the formic acid decomposition catalyst layer 13. Since the formic acid decomposition catalyst layer 13 is provided on the top of the convex surface of the separator, proton conductivity is ensured by contacting the solid polymer electrolyte membrane of the anode catalyst layer and the formic acid decomposition catalyst layer at this portion.

  By adopting such a configuration, it is possible to decompose formic acid which is a reaction by-product on the separator surface, and it is possible to provide a stacked fuel cell with a small amount of formic acid discharged over a long period of time.

  Another embodiment of the present invention will be described. FIG. 6 is a view schematically showing a cross section taken along the line AA 'of the separator 1 shown in FIG. When methanol is used as fuel, methanol permeates the electrolyte membrane and reaches the cathode, and formic acid is generated as a reaction by-product at the cathode. Since air is supplied to the cathode, formic acid can be oxidized with oxygen in the air. Thus, unlike the anode, there is no need to electrochemically oxidize formic acid. Therefore, at the cathode, the formic acid decomposition catalyst layer 13 can be formed on the outer surface of the separator in the flow path portion where the reactant other than the top of the convex surface that requires electrical conductivity in the separator 1 flows. The formic acid decomposition catalyst layer 13 is prepared by kneading a catalyst metal or a catalyst such as carbon, ceramics, or metal powder supporting the catalyst metal and a resin binder for fixing the catalyst, and then applying the mixture, thereby applying the formic acid decomposition catalyst layer 13. Layer 13 was formed. The formic acid decomposition catalyst layer 13 is preferably a catalyst such as platinum, ruthenium, osmium, palladium, tungsten, molybdenum, iron, cobalt, nickel, manganese, etc. that promotes the formic acid oxidation reaction. Further, it is preferable that these formic acid oxidation catalysts are supported as fine particles on a carrier in the same manner as described above. This is because the catalyst metal can be used as smaller fine particles by being supported on the carrier, and the specific surface area is increased. Further, since it is not necessary to oxidize formic acid electrochemically, it is not necessary to use a solid polymer electrolyte as the binder.

  By adopting such a configuration, it is possible to decompose formic acid which is a reaction by-product on the separator surface, and it is possible to provide a stacked fuel cell with a small amount of formic acid discharged over a long period of time. FIG. 6 shows an example in which the formic acid decomposition catalyst layer 13 is formed only in the flow path portion in which the reactant other than the top of the convex surface in the separator 1 flows, but the formic acid decomposition catalyst layer 13 is also formed on the top of the convex surface. May be. In the cathode-side separator, when the formic acid decomposition catalyst layer 13 is formed on the top of the convex surface, the generated water generated at the cathode is diffused toward the formic acid decomposition catalyst layer 13 to prevent flooding due to the generated water at the cathode. Can also be expected.

  Another embodiment of the present invention will be described. Depending on the type of metal, the separator 1 may not have sufficient long-term stability in the first-described embodiment. If the separator 1 does not have sufficient corrosion resistance, such as magnesium or zinc, significant corrosion occurs and causes deterioration of the battery. Therefore, it is preferable that the metal selected as the separator 1 has a certain degree of corrosion resistance. Of these, titanium, zirconium, tantalum, niobium, and tungsten are highly corrosion-resistant metals, and at the same time, the amount of corrosion products released is extremely small compared to other metals. This is because the corrosion product has a property of staying on the surface as an oxide film. Therefore, the adverse effect on the electrode and the electrolyte membrane is small, and is a preferable metal in the fuel cell.

  Aluminum has poor corrosion resistance compared to the above metals, but even if it corrodes, a film having the same quality as alumite is produced, so the amount of corrosion products released is relatively small.

  By selecting such a metal as the separator 1, it is possible to expect a long-life separator in which elution of metal ions is reduced and deterioration of the MEA 7 can be minimized.

  Another embodiment of the present invention will be described. Among the metals used for the separator 1, there are expensive metals. Therefore, the separator 1 is made of a composite metal material having a center layer and a surface layer, and the intermediate layer is made of iron, aluminum, copper, titanium, magnesium, zirconium, tantalum, niobium, tungsten, nickel, chromium, and alloys of the metals. By using an inexpensive metal and disposing an expensive metal as a thin film on the surface layer, it can be expected to reduce the amount of the expensive metal used.

  Another embodiment of the present invention will be described. When a cell is manufactured in the above-described manner, the initial power generation characteristics may be low, or the difference in cell voltage for each cell may be large. This is because the electrical contact between the separator 1 and the reaction byproduct decomposition catalyst layer 12 is not good. Therefore, as shown in FIG. 7, between the separator 1 and the reaction by-product decomposition catalyst layer 12 in the porous layer 11, cobalt, nickel, copper, zinc, etc. are formed by plating, vapor deposition, sputtering, CVD, or the like. A metal layer 14 such as chromium, tin, ruthenium, rhodium, palladium, silver, osmium, iridium, gold and alloys thereof is formed. Thereby, it can be expected that the electrical contact between the separator 1 and the reaction byproduct decomposition catalyst layer 12 is improved, the power generation characteristics are improved, and the difference in the power generation characteristics for each cell is reduced.

  Another embodiment of the present invention will be described. Depending on the type of metal, the metal layer 14 may not have sufficient long-term stability in the first-described embodiment. This is because when the metal layer 14 does not have sufficient corrosion resistance such as iron, cobalt, nickel, copper, zinc, and tin, remarkable corrosion occurs and causes deterioration of the battery. Therefore, it is preferable that the metal selected as the metal layer 14 has a certain degree of corrosion resistance and conductivity. Ruthenium, rhodium, palladium, silver, osmium, iridium and gold selected as such metals are expensive materials. Therefore, as shown in FIG. 8, iron, cobalt, nickel, copper, zinc, chromium, tin, silver and alloys of these metals are arranged on the separator 1 side, and an expensive metal is arranged in a thin film on the outside, It can be expected that the amount of expensive metal used is reduced and high objectivity is obtained.

  Another embodiment of the present invention will be described. The metal used for the outermost layer of the separator 1 can easily form the porous layer 11 by anodizing treatment. In addition, the pore shape and the thickness of the porous layer can be arbitrarily controlled by setting conditions such as an anodizing bath, current, and voltage. As a result, it becomes possible to improve the diffusion of the reaction gas to the MEA 7 and the discharge of the generated water, and it can be expected that the power generation characteristics and the life characteristics are improved.

  If the thickness of the reaction product decomposition layer 12 is greater than 200 μm, it becomes difficult to diffuse reaction gas into the reaction product catalyst layer 12 or discharge the generated water, resulting in a decrease in power generation characteristics. If the thickness is 200 μm or less, the power generation characteristics are sufficiently maintained.

  A specific embodiment of the present invention will be described by taking a methanol fuel cell using methanol as a fuel as an example. The example which uses aluminum (A5052) for the metal plate for the separator 1 is shown. In order to form a channel groove with an aluminum thickness of 0.3 mm of the coiled thin plate, the separator 1 is processed by an extrusion press to have an uneven shape on both sides of the flat portion and the central portion. At the same time, punching is performed to form the manifold 4. Thereby, the thing of the shape equivalent to the separator 1 shown in FIG. 1 can be manufactured.

  Next, a method for forming the porous layer 11 on the processed separator 1 will be described. Prior to forming the porous layer 11 by anodic oxidation, blasting is performed for scale removal according to the surface state of the separator 1 after processing, followed by degreasing with alkali or an organic solvent. Next, polishing, acid cleaning, and alkali cleaning are performed to remove the oxide film. Thereafter, an anodic oxidation treatment was performed to form the porous layer 11.

  In the anodizing treatment, 3 to 10% oxalic acid was used in the electrolytic bath, the voltage was 30 to 100 V, the temperature was 10 ° C. or less, the treatment time was 20 to 120 minutes, and the film thickness was 20 to 50 μm.

The slurry used for the formic acid decomposition functional layer of the anode is prepared by mixing palladium supported on carbon black, Nafion (hereinafter, registered trademark), which is a solid polymer electrolyte, propanol, and water, and using a stirrer for 24 hours. Stir. This slurry was spray-coated on the surface of the separator so that the mass of palladium was 0.4 mg / cm ^2, and then held in a constant temperature bath at 120 ° C. for 1 hour to adhere the formic acid decomposition catalyst layer to the separator. An anode separator was prepared.

As the cathode separator, a fuel cell was formed by using a separator without a formic acid decomposition catalyst layer that had been cut.
From the measurement results, the thickness of the formic acid decomposition catalyst layer was approximately 40 μm.

  A specific embodiment of the present invention will be described by taking a methanol fuel cell using methanol as a fuel as an example. The example which uses aluminum (A5052) for the metal plate for the separator 1 is shown. In order to form a channel groove with an aluminum thickness of 0.3 mm of the coiled thin plate, the separator 1 is processed by an extrusion press to have an uneven shape on both sides of the flat portion and the central portion. At the same time, punching is performed to form the manifold 4. Thereby, the thing of the shape equivalent to the separator 1 shown in FIG. 1 can be manufactured.

  Next, a method for forming the porous layer 11 on the processed separator 1 will be described. Prior to forming the porous layer 11 by anodic oxidation, blasting is performed for scale removal according to the surface state of the separator 1 after processing, followed by degreasing with alkali or an organic solvent. Next, polishing, acid cleaning, and alkali cleaning are performed to remove the oxide film. Thereafter, an anodic oxidation treatment was performed to form the porous layer 11.

  In the anodizing treatment, 3 to 10% oxalic acid was used in the electrolytic bath, the voltage was 30 to 100 V, the temperature was 10 ° C. or less, the treatment time was 20 to 120 minutes, and the film thickness was 20 to 50 μm.

The slurry used for the formic acid decomposition catalyst layer of the cathode was prepared by mixing platinum supported on carbon black, vinylidene fluoride as a binder, and N-methyl-2-pyrrolidone as a solvent. This slurry was masked on the ribs of the separator so that the mass of platinum was 0.4 mg / cm ² , sprayed only on the surface of the flow path, and then held in a constant temperature bath at 140 ° C. for 3 hours. The decomposition catalyst layer was brought into close contact with each other to produce a cathode separator according to this example.

As the anode separator, a fuel cell was formed by using a separator without a formic acid decomposition catalyst layer that had been cut.
From the measurement results, the thickness of the formic acid decomposition catalyst layer was approximately 30 μm.

  A fuel cell was constructed using the anode separator with a formic acid decomposition functional layer of Example 1 and the cathode separator with a formic acid decomposition functional layer of Example 2.

[Comparative Example 1]
As a comparative example, a separator with a power generation area of 25 cm ² using a dense graphite as a material and cutting a 1 mm wide gas flow path having a width of 1 mm and a depth of 1 mm and a 1 mm rib contacting the electrode with an anode separator and a cathode separator. A fuel battery cell was constructed.

[Evaluation]
The MEA used for the evaluation of the fuel cell was produced as follows. Platinum ruthenium supported on carbon black, Nafion, which is a solid polymer electrolyte, propanol, and water were mixed to prepare an anode slurry, which was stirred with a stirrer for 24 hours. Further, platinum supported on carbon black, Nafion, propanol, and water were mixed to prepare a slurry for the cathode, and stirred for 24 hours with a stirrer.

  Next, the anode slurry was spray-coated on the solid polymer electrolyte membrane, the cathode slurry was spray-coated on the other surface of the solid polymer electrolyte membrane, and then hot pressed at 120 ° C. Here, sulfonated polyether sulfone was used for the solid polymer electrolyte membrane.

  Using the MEA produced as described above, carbon paper for the anode diffusion layer and carbon cloth for the cathode diffusion layer, the separators shown in the examples and comparative examples are arranged on both sides thereof, and tightened at a predetermined pressure, thereby fuel. A battery cell was assembled.

Here, the amount of formic acid discharged was measured by collecting the discharged aqueous methanol solution and exhaust gas with ice water and measuring the formic acid contained therein by ion chromatography. The supplied aqueous methanol solution was an aqueous solution containing 3% by weight of methanol, and air with a relative humidity of 60% was supplied to the cathode. The cell temperature was 60 ° C. and the load current density was 0.15 A / cm ² . Table 1 shows the results.

  Compared with the separator having no formic acid decomposition catalyst layer of Comparative Example 1, the formic acid discharge amount was about 1/260 in the separator having the formic acid decomposition layer on the anode and cathode of Example 3 being very small. In Examples 1 and 2, the amount of formic acid discharged was about 8 times different. This indicates that since the amount of formic acid produced in the anode is larger than that in the cathode, the total amount of formic acid discharged cannot be greatly reduced when the formic acid decomposition layer is provided only on the cathode.

1 Separator 2 Flat part 3 Distribution part 4 Manifold 5 Gasket 7 MEA
8 Current collector plate 9 Insulating plate 10 End plate 11 Porous layer 12 Reactive biodegradation catalyst layer 13 Formic acid decomposition catalyst layer 14 Metal layer 101 Separator with gasket

Claims (11)

A membrane electrode assembly in which a pair of anode and cathode electrodes are disposed on both surfaces of the electrolyte, and a pair of separators disposed on both sides of the membrane electrode assembly as a unit cell, and a stacked type in which a plurality of the unit cells are stacked In fuel cells,
A porous layer is provided on a surface of the separator in contact with the anode electrode, and the porous layer includes a catalyst made of at least one metal selected from palladium, iridium, rhodium and an alloy of the metal. A laminated fuel cell, wherein a formic acid decomposition catalyst layer is formed.   2. The stacked fuel cell according to claim 1, wherein a porous layer is provided on a surface of the separator facing the cathode electrode, and the catalyst for decomposing formic acid is contained inside the porous layer. A layered fuel cell, wherein a layer is formed.   3. The stacked fuel cell according to claim 1, wherein the first formic acid decomposition catalyst layer includes a conductive material supporting the catalyst and a binding material having proton conductivity for binding the conductive material. A laminated fuel cell characterized by being made.   4. The stacked fuel cell according to claim 1, wherein a single-layer or multiple-layer metal conductive layer is formed between the first catalyst layer and a metal constituting the separator. 5. Stacked fuel cell.   5. The stacked fuel cell according to claim 1, wherein the metal constituting the separator is aluminum, titanium, magnesium, zirconium, tantalum, niobium, tungsten, hafnium, zinc, bismuth, antimony, and an alloy of the metal. A laminated fuel cell comprising at least one metal selected from the group consisting of:   5. The stacked fuel cell according to claim 1, wherein the separator is made of a composite metal material having a center layer and a surface layer, and the metal constituting the center layer is iron, aluminum, copper, titanium, It consists of at least one metal selected from magnesium, zirconium, tantalum, niobium, tungsten, nickel, chromium and alloys of the metal, and the metal constituting the surface layer is aluminum, titanium, magnesium, zirconium, tantalum, niobium, tungsten , Hafnium, zinc, bismuth, antimony and at least one metal selected from these alloys.   5. The stacked fuel cell according to claim 4, wherein the metal conductive layer is selected from iron, cobalt, nickel, copper, zinc, chromium, tin, ruthenium, rhodium, palladium, silver, osmium, iridium, gold, and alloys thereof. A laminated fuel cell comprising at least one kind of metal.   5. The stacked fuel cell according to claim 4, wherein the metal conductive layer has at least one selected from ruthenium, rhodium, palladium, silver, osmium, iridium, gold, and an alloy of the metal on the first formic acid decomposition catalyst layer side. A laminated fuel cell comprising a metal of a kind, wherein the separator side is made of at least one metal selected from iron, cobalt, nickel, copper, zinc, chromium, tin, silver and alloys of the metal.   9. The stacked fuel cell according to claim 1, wherein the porous layer of the separator is formed by an anodic oxidation process.   10. The stacked fuel cell according to claim 1, wherein the first formic acid decomposition catalyst layer or the second formic acid decomposition catalyst layer has a thickness of 200 μm or less. Fuel cell.   The stacked fuel cell according to claim 1, wherein power is generated using a fuel containing methanol.