JP2012212564A - Fuel cell separator and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of conventional fuel cells that measures are not taken for reducing the contact resistance of a separator and improving the corrosion resistance through the surface treatment.SOLUTION: A cathode side separator 3A separates a cathode gas passage Cg from a coolant passage Cf in a fuel cell C. A conductive coat is formed on a surface of the separator, and the thickness of the conductive coat is increased at an outlet port side of a cathode gas relative to an inlet port side on a surface of the cathod gas passage Cg side. Further, the thickness of the conductive coat is increased at an outlet port side of a coolant relative to an inlet port side on a surface of the coolant passage Cf side. This structure achieves both the efficient reduction of the contact resistance and the improvement of the corrosion resistance.

Description

  The present invention relates to a fuel cell separator used for isolating a reaction gas flow path and a coolant flow path in a fuel cell, and a fuel cell including the separator as a constituent element.

  An example of this type of fuel cell is described in Patent Document 1. The fuel cell described in Patent Document 1 includes a membrane electrode assembly (MEA) in which an electrolyte membrane is sandwiched between an air electrode and a fuel electrode, and a cathode separator and an anode separator that sandwich the membrane electrode structure. Yes. Each separator forms an air flow path and a fuel flow path between the separator and the membrane electrode structure, and forms a refrigerant flow path between adjacent fuel cells when stacked.

  And said fuel cell comprises at least one separator by an electroconductive part (base material) and an insulation part (coating), and thickens the thickness of an insulation part as a part with high possibility of being plugged up with water, The heat conductivity of the portion is lowered to promote heat generation, thereby suppressing flooding.

JP 2006-134698 A

  Incidentally, the separator in this type of fuel cell functions as a conductive member as described in Patent Document 1 in addition to isolating the reaction gas flow path and the coolant flow path. Therefore, the separator described in Patent Document 1 is made of a material having a small electrical resistance.

  However, in the conventional fuel cell, although the separator is made of a material having a small electric resistance as described above, it is necessary to consider further improvement of the corrosion resistance of the separator against the reaction gas and the coolant.

  The present invention has been made in view of the above-described conventional situation, and an object of the present invention is to provide a fuel cell separator and a fuel cell that can achieve both efficient reduction of contact resistance and improvement of corrosion resistance. .

  The fuel cell separator of the present invention is a cathode-side separator that separates the cathode gas flow path and the coolant flow path in the fuel cell.

  The fuel cell separator has a conductive film formed on the surface thereof, and on the surface on the cathode gas flow path side, the thickness of the conductive film is increased on the outlet side than on the cathode gas inlet side, and cooling is performed. In the surface on the liquid flow path side, the conductive film is thicker on the outlet side than on the inlet side of the cooling liquid.

  The fuel cell of the present invention has a structure in which a membrane electrode structure is sandwiched between a pair of separators, and a fuel that forms a coolant flow path between adjacent separators (separators of adjacent fuel cells) in a stacked state It is a battery.

  In the fuel cell, a conductive coating is formed on the surface of the cathode-side separator that separates the cathode gas flow channel and the coolant flow channel, and the conductive coating is one of the separators forming the cathode gas flow channel. In the surface, the film thickness on the outlet side is made thicker than the film thickness on the inlet side of the cathode gas, and on the other surface of the separator forming the coolant flow path, the film thickness on the inlet side of the coolant is made larger. It is characterized in that the outlet side film is formed thick.

  Here, on the cathode side of the fuel cell, the current density increases as it becomes closer to the cathode gas inlet side, and the contact resistance decreases as the thickness of the conductive film decreases at the higher current density. Therefore, in the fuel cell separator and the fuel cell described above, on one side of the separator forming the cathode gas flow path, the conductive film is thicker on the outlet side than on the cathode gas inlet side (on the inlet side). As a whole, the contact resistance between the cathode separator and the membrane electrode structure is efficiently reduced.

  Further, in the coolant flow path, the temperature becomes higher as it becomes the outlet side of the coolant, and corrosion tends to occur as the temperature becomes higher. Therefore, in the fuel cell separator and the fuel cell described above, the other surface of the separator that forms the coolant flow path is formed by increasing the thickness of the conductive coating on the outlet side rather than on the coolant inlet side. As corrosion resistance is improved.

  According to the fuel cell separator and the fuel cell of the present invention, by adopting the above configuration, it is possible to achieve both efficient reduction of contact resistance and improvement of corrosion resistance.

It is a top view of the decomposition | disassembly state explaining one embodiment of the separator for fuel cells of this invention, and a fuel cell. It is a top view after the assembly of the fuel cell shown in FIG. It is the disassembled perspective view (A) explaining the fuel cell stack formed by laminating | stacking the fuel cell shown in FIG. 1, and the perspective view (B) after an assembly. It is sectional drawing of the principal part of a fuel cell stack. It is explanatory drawing which shows the flow direction of the cathode gas in a cathode side separator, the flow direction of a cooling fluid, and the film thickness distribution of an electroconductive film. It is explanatory drawing which shows the surface by the side of the anode gas flow path in an anode side separator, and the film thickness distribution of a conductive film as other embodiment of the separator for fuel cells of this invention, and a fuel cell. FIG. 6 is an explanatory view showing a coolant flow path side surface in an anode side separator and a film thickness distribution of a conductive coating as still another embodiment of a fuel cell separator and a fuel cell of the present invention. It is explanatory drawing which shows the flow direction of cathode gas and anode gas, and the film thickness distribution of an electroconductive film as other embodiment of the separator for fuel cells of this invention, and a fuel cell. It is explanatory drawing which shows formation of the conductive film by sputtering, and film thickness distribution of a conductive film as one Embodiment of the manufacturing method of the separator of this invention.

  1 and 2 are diagrams illustrating an embodiment of a fuel cell separator and a fuel cell according to the present invention.

  The illustrated fuel cell C has a structure in which the membrane electrode structure 2 is sandwiched between a pair of separators 3A and 3B. In particular, the fuel cell C of the embodiment shown in FIG. 1 includes a membrane electrode structure 2 having a frame 1 around it, and cathode-side and anode-side separators 3A and 3B that sandwich the membrane electrode structure 2 together with the frame 1. I have. The frame 1 has a thin plate shape with a substantially constant thickness, and most of the frame 1 except the edge is thinner than the thickness of the membrane electrode structure 2. And it has the distribution area (diffuser part mentioned below) which distributes the gas for reaction between frame 1 and both separators 3A and 3B. It is desirable in manufacturing that the frame 1 is a resin and the separators 3A and 3B are metal.

  The membrane electrode structure 2 is generally called MEA (Membrane Electrode Assembly), and has a structure in which an electrolyte layer made of a solid polymer is sandwiched between an air electrode layer (cathode) and a fuel electrode layer (anode), for example. Have. In the membrane electrode structure 2, a cathode gas (air) that is one reaction gas is supplied to the air electrode layer, and an anode gas (hydrogen) that is the other reaction gas is supplied to the fuel electrode layer. It generates electricity by electrochemical reaction. The membrane electrode structure 2 includes those having a gas diffusion layer made of carbon paper or a porous body on the surfaces of the air electrode layer and the fuel electrode layer.

  The frame 1 is integrated with the membrane electrode structure 2 by resin film or resin molding. In this embodiment, the frame 1 has a rectangular shape with the membrane electrode structure 2 at the center. The frame 1 has three manifold holes H1 to H6 arranged at both ends, and a region from each manifold hole group to the membrane electrode structure 2 serves as a reaction gas flow region. Both the frame 1 and the separators 3A and 3B have a rectangular plate shape having substantially the same vertical and horizontal dimensions.

  Each of the separators 3A and 3B is made of stainless steel as a more preferable embodiment, and thereby has low cost and high corrosion resistance. In each of the separators 3A and 3B, a central portion corresponding to the membrane electrode structure 2 is formed in a wave shape in a cross section in the short side direction. This wave shape is continuous in the long side direction as shown in the figure. Thereby, each separator 3A, 3B has each convex part in contact with the membrane electrode structure 2 in the central part corresponding to the membrane electrode structure 2 in the waveform, and each concave part in the waveform has the reaction gas. It becomes a flow path. This gas flow path will be described later.

  Further, each separator 3A, 3B has manifold holes H1 to H6 equivalent to the manifold holes H1 to H6 of the frame 1 at both ends, and the region extending from each manifold hole group to the corrugated section is a reaction gas. Distribution area.

  The frame 1 and the membrane electrode structure 2 and the separators 3A and 3B are overlapped to constitute the fuel cell C. At this time, as shown in FIG. 2, the fuel cell C includes a power generation unit G that is a region of the membrane electrode structure 2 at the center. Further, on both sides of the power generation unit G, manifold units M and M that supply and discharge the reaction gas, and diffuser units D and D that are reaction gas flow regions from each manifold unit M to the power generation unit G are provided. It has become.

  Here, the diffuser portion D, which is the reaction gas flow region, is not only between both ends of the fuel cell C in FIG. 2, but also between the frame 1 and the separators 3A and 3B on both sides, that is, on the anode and cathode sides. Each is formed.

  In one manifold section M shown on the left side of FIG. 2, each of the manifold holes H1 to H3 is for cathode gas supply (H1), coolant supply (H2), and anode gas discharge (H3). Each flow path is formed in communication with each other. In the other manifold portion M shown on the right side of FIG. 2, the manifold holes H4 to H6 are for anode gas supply (H4), coolant discharge (H5), and cathode gas discharge (H6), and are laminated. Each flow path is formed in communication with each other in the direction.

  That is, in this embodiment, the cathode gas, the anode gas, and the coolant flow in one direction along the long sides of the separators 3A and 3B having a rectangular plate shape. In this embodiment, the flow directions of the cathode gas and the coolant are the same (rightward in FIG. 1), and the flow directions of the cathode gas and the anode gas are opposite to each other.

  Furthermore, as shown in FIG. 1, the fuel cell C is provided with a gas seal SL between the edges of the frame 1 and the separators 3A and 3B or around the manifold holes H1 to H6. In a state where a plurality of fuel cells C are stacked, a gas seal SL is also provided between the fuel cells C, that is, between the adjacent separators 3A and 3B. In this embodiment, the coolant is circulated between the adjacent separators 3A and 3B. This coolant flow path will be described later.

  The above gas seal SL hermetically separates the flow regions of the cathode gas, the anode gas, and the cooling liquid between the individual layers, and allows the predetermined fluid to flow between the layers. Openings are provided at appropriate locations on the periphery.

  The fuel cell C having the above-described configuration is formed by stacking a plurality of sheets to form a fuel cell stack FS as shown in FIG.

  As shown in FIG. 3A, the fuel cell stack FS has a current collector plate 4A and a spacer 5 at one end (the right end in FIG. 3) in the stacking direction of the stack A of the fuel cells C. The end plate 6A is provided via the current collector, and the end plate 6B is provided at the other end via the current collector plate 4B. Further, the fuel cell stack FS is provided with fastening plates 7A and 7B on both sides (upper and lower surfaces in FIG. 3) on the long side of the fuel cell C with respect to the laminate A, and on the short side. Reinforcing plates 8A and 8B are provided on both sides.

  In the fuel cell stack FS, the fastening plates 7A and 7B and the reinforcing plates 8A and 8B are connected to both end plates 6A and 6B by bolts B. In this way, the fuel cell stack FS has a case-integrated structure as shown in FIG. 3B, and the stacked body A is restrained and pressed in the stacking direction so that each fuel cell C has a predetermined contact surface pressure. In order to maintain good gas sealing properties and conductivity.

  In this manner, the fuel cell separators 3A and 3B and the fuel cell C form the cathode gas flow path Cg between the membrane electrode structure 2 and the cathode side separator 3A as shown in FIG. An anode gas flow path Ag is formed between the membrane electrode structure 2 and the anode side separator 3B. Further, in the fuel cell stack FS described above, a coolant flow path Cf is formed between adjacent fuel cells C (adjacent separators 3A and 3B).

  That is, in the fuel cell stack FS, the cathode-side separator 3A isolates the cathode gas channel Cg and the coolant channel Cf. On the other hand, the anode-side separator 3B isolates the anode gas channel Ag and the cooling channel Cf.

  In the fuel cell separators 3A and 3B and the fuel cell C, as shown in FIG. 5, a conductive coating is formed on the surface of the cathode side separator 3A. At this time, on the cathode side, as indicated by arrows in the figure, the flow directions of the cathode gas and the coolant are the same. On the other hand, as shown in the film thickness distribution in the figure, the separator 3A has a conductive coating on one side (MEA surface) forming the cathode gas flow path Cg on the outlet side rather than on the cathode gas inlet side. Increase the film thickness (thinner on the inlet side). In addition, on the other surface (cooling liquid surface) forming the cooling liquid flow path Cf, the film thickness of the conductive coating is made thicker on the outlet side than on the cooling liquid inlet side.

  In addition, although separator 3A, 3B shown in FIGS. 5-9 differs in the form from what is shown in FIGS. 1-3, since the basic composition is equivalent, the same code | symbol is attached | subjected to the same site | part.

  As the conductive film, for example, a hard carbon film is used, and diamond-like carbon can be used as a more preferable film, and can be formed by sputtering as described later. As a result, a conductive film having low cost and high corrosion resistance can be obtained.

  Examples of the material for the conductive coating include polycrystalline graphite, graphite block (highly crystalline graphite), carbon black, fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, and carbon fibril. Specific examples of carbon black include ketjen black, acetylene black, channel black, lamp black, oil furnace black, or thermal black. Carbon black may be subjected to a graphitization treatment.

  These carbon materials may be used in combination with a resin such as a polyester resin, an aramid resin, or a polypropylene resin. Examples of materials other than the carbon material included in the conductive coating include gold (Au), silver (Ag), platinum (Pt), ruthenium (Ru), palladium (Pd), rhodium (Rh), and indium (In). A noble metal such as polytetrafluoroethylene (PTFE), a conductive oxide, and the like. As for materials other than polycrystalline graphite, only 1 type may be used and 2 or more types may be used together.

  The average thickness of the conductive coating is preferably 1 nm to 1000 nm, more preferably 2 nm to 500 nm, and still more preferably 5 nm to 200 nm. If the thickness of the conductive coating is a value within such a range, sufficient conductivity can be ensured between the gas diffusion substrate and the separators 3A and 3B. Moreover, a high corrosion resistance function can be given to the base material (stainless steel) of the separators 3A and 3B.

  Here, on the cathode side of the fuel cell C, the current density increases as the cathode gas becomes closer to the inlet side, and the contact resistance decreases as the thickness of the conductive film decreases at the higher current density. Therefore, in the cathode side separator 3A and the fuel cell C described above, the film thickness of the conductive coating on the one side (MEA surface) of the separator 3A that forms the cathode gas flow path Cg is closer to the outlet side than the inlet side of the cathode gas. By thickening (thinning on the inlet side), the contact resistance between the separator 3A and the membrane electrode structure 2 is efficiently reduced as a whole.

  Further, in the coolant flow path Cf, the temperature becomes higher as it becomes the outlet side of the coolant, and the temperature becomes higher and the corrosion tends to occur. Therefore, in the cathode side separator 3A and the fuel cell C described above, on the other surface of the separator 3A that forms the coolant channel Cf, the thickness of the conductive coating is made thicker on the outlet side than on the coolant inlet side. As a whole, the corrosion resistance is improved.

  Thus, according to the cathode side separator 3A and the fuel cell C described above, it is possible to achieve both an efficient reduction in contact resistance and an improvement in corrosion resistance. In addition, by making the flow directions of the cathode gas and the coolant the same direction, the overall performance is higher due to the combination of the conductive performance and the cooling performance, and the current density distribution is also on the cathode gas inlet side. Since it is biased, the effect of reducing the contact resistance is more exhibited.

  FIG. 6 is a view for explaining another embodiment of the fuel cell separator and the fuel cell of the present invention. In this embodiment, a conductive film is formed on the surface of the anode-side separator 3B. In this case, on one surface (MEA surface) of the separator 3B forming the anode gas flow path Ag, the inlet thereof is shown in the film thickness distribution in the figure with respect to the flow direction of the cathode gas indicated by the arrow in the figure. The thickness of the conductive coating is increased on the outlet side than on the side. That is, the anode-side separator 3B sets the film thickness of the conductive coating on the basis of the cathode gas flow direction regardless of the anode gas flow direction.

  According to the anode separator 3B and the fuel cell C described above, the thickness of the conductive coating is reduced on the cathode entrance side where the current density is high, so that the contact resistance between the anode separator 3B and the membrane electrode structure 2 is improved. Therefore, the conductive performance and the power generation performance can be improved.

  FIG. 7 is a view for explaining still another embodiment of the fuel cell separator and the fuel cell of the present invention. In this embodiment, a conductive film is formed on the surface of the anode-side separator 3B, and the other surface (cooling liquid surface) of the separator 3B that forms the cooling liquid flow path Cf is on the outlet side rather than the inlet side of the cooling liquid. The thickness of the conductive coating is increased. Also in this case, the anode-side separator 3B sets the film thickness of the conductive coating on the basis of the coolant flow direction regardless of the anode gas flow direction.

  According to the anode separator 3B and the fuel cell C described above, the coolant flow path Cf has a higher temperature toward the coolant outlet side and is more likely to corrode as the temperature increases. By increasing the film thickness of the conductive coating on the outlet side rather than on the side, the overall corrosion resistance can be improved.

  FIG. 8 is a view for explaining still another embodiment of the fuel cell separator and the fuel cell of the present invention. In this embodiment, the flow directions of the cathode gas and the anode gas are opposite to each other. In this case, in the cathode side separator 3A, as in the previous embodiment (see FIG. 5), the film thickness of the conductive coating is formed to be thicker on the outlet side than on the cathode gas inlet side.

  On the other hand, in the anode side separator 3B, the film thickness on the outlet side is made thicker than the film thickness on the inlet side of the sword gas with reference to the flow direction of the cathode gas as described above. Therefore, the conductive film in the cathode side separator 3A and the conductive film in the anode side separator 3B have the same film thickness distribution shown in the figure.

   According to the separators 3A and 3B and the fuel cell C, it is possible to achieve both efficient reduction of contact resistance and improvement of corrosion resistance, as in the previous embodiment. Moreover, if the flow directions of the cathode gas and the anode gas are opposite to each other, the power generation performance is improved, and the current density distribution is biased toward the inlet side of the cathode gas, so that the effect of reducing the above contact resistance can be exhibited more. It becomes.

  FIG. 9 is a diagram illustrating a method for manufacturing the separators 3A and 3B described in the above embodiments. In the manufacturing method, a plurality of separators are arranged symmetrically with respect to a center point facing the sputtering target TG or a center line CL including the center point so that one end portion in the long side direction is the center side. To do. In the illustrated example, the two cathode-side separators 3A and 3A are symmetrically disposed in the chamber of the sputtering apparatus with the end portion serving as the cathode gas outlet side facing the center line CL.

  Then, sputtering using the target RG is performed. That is, an inert gas (for example, Ar gas) ionized by applying a high voltage to the target TG is collided, and atoms on the surface of the target TG are repelled to form conductive films on both surfaces of the separators 3A and 3A. . Thereafter, a conductive film is similarly formed on the back surface of each separator 3A.

  When the separators 3A and 3A are arranged and sputtering is performed as described above, as shown in the film thickness distribution in the figure, the portion close to the target TG, that is, the end portion on the cathode gas outlet side of each separator 3A and 3A. Thus, the film thickness of the conductive film increases, and the film thickness decreases toward the inlet side. Thereby, the cathode side separator 3A described in FIG. 5 is obtained.

  Thus, according to the separator manufacturing method described above, a single target TG can be used, and a plurality of separators 3A and 3A in which the film thickness of the conductive coating gradually changes can be manufactured simultaneously. Improvement and reduction of manufacturing costs. In addition, this separator manufacturing method is very effective for forming a film on the elongated rectangular plate-shaped separator illustrated in each embodiment.

  In the above manufacturing method, the separator can be arranged in various forms. For example, a plurality of separators can be arranged on both sides of the center line CL, or a plurality of separators can be arranged radially with respect to the center point, and a roll-like material can be used to feed out the material. It is also possible to form a conductive film while punching the separator from the material.

  The separator for a fuel cell and the fuel cell of the present invention are not limited to the above-described embodiments, and the details of the configuration can be appropriately changed without departing from the gist of the present invention. It is also possible to combine the configurations of the embodiments.

Ag anode gas channel Cg cathode gas channel Cf coolant channel C fuel cell FS fuel cell stack TG target 2 membrane electrode structure 3A cathode side separator 3B anode side separator

Claims (15)

A cathode separator that separates a cathode gas flow path and a coolant flow path in a fuel cell,
A conductive film is formed on the surface,
On the cathode gas flow path side surface, the conductive film is made thicker on the outlet side than on the cathode gas inlet side,
A separator for a fuel cell, characterized in that on the surface on the coolant flow path side, the thickness of the conductive coating is increased on the exit side than on the coolant entrance side. An anode-side separator that separates an anode gas passage and a coolant passage in a fuel cell,
A conductive film is formed on the surface,
A separator for a fuel cell, characterized in that on the surface on the anode gas flow path side, the thickness of the conductive coating is made thicker on the outlet side than on the inlet side with respect to the flow direction of the cathode gas.   3. The fuel cell separator according to claim 2, wherein, on the surface on the coolant flow path side, the film thickness of the conductive coating is made thicker on the exit side than on the coolant entrance side.   The fuel cell separator according to any one of claims 1 to 3, wherein the separator is made of stainless steel.   The fuel cell separator according to any one of claims 1 to 4, wherein the conductive coating is diamond-like carbon.   6. The fuel cell separator according to claim 1, wherein the fuel cell separator has a rectangular plate shape and a direction along a long side thereof is a flow direction of a gas and a coolant. A fuel cell having a structure in which a membrane electrode structure is sandwiched between a pair of separators, and forming a coolant channel between adjacent separators in a stacked state,
A conductive coating is formed on the surface of the cathode-side separator that separates the cathode gas channel and the coolant channel,
The separator on which one side of the separator that forms the cathode gas flow path has a larger thickness on the outlet side than the film thickness on the inlet side of the cathode gas and the conductive film forms the coolant flow path. On the other side of the fuel cell, a film thickness on the outlet side is formed thicker than a film thickness on the inlet side of the coolant. A conductive coating is formed on the surface of the anode separator that separates the anode gas passage and the coolant passage,
The conductive film is characterized in that on one surface of the separator forming the anode gas flow path, the film thickness on the outlet side is made larger than the film thickness on the inlet side in the flow direction of the cathode gas. The fuel cell according to claim 7.   9. The conductive film is formed on the other surface of the separator forming the coolant flow path so that the film thickness on the outlet side is greater than the film thickness on the inlet side of the coolant. A fuel cell according to claim 1.   The fuel cell according to claim 7, wherein the flow direction of the cathode gas and the flow direction of the coolant are the same.   11. The fuel cell according to claim 7, wherein the flow direction of the cathode gas and the flow direction of the anode gas are opposite to each other.   The fuel cell according to any one of claims 7 to 11, wherein the separator is made of stainless steel.   The fuel cell according to any one of claims 7 to 12, wherein the conductive coating is diamond-like carbon.   The fuel cell according to any one of claims 7 to 13, wherein the separator has a rectangular plate shape, and gas and coolant are circulated in a direction along a long side thereof. In manufacturing the fuel cell separator according to claim 6 or the fuel cell separator according to claim 14,
A plurality of separators are symmetrically arranged with respect to a center point or a center line facing the sputtering target so that one end portion in the long side direction is a center side, and sputtering using the target in this state A process for producing a separator, wherein a conductive film is formed on each separator.

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